1. Field of the Invention
The present invention relates to a color filter for a liquid crystal display (LCD), and more particularly to a color filter that is adapted to be changeably used for a twisted nematic (TN) mode LCD and in a plane switching (IPS) mode LCD by forming a light-shielding layer at the rear side of a transparent substrate to improve surface morphology.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) includes switching devices constituted by thin film transistors, each of which consists of a gate electrode, a gate insulating film, an active layer, an ohmic contact layer, source and drain electrodes, and a liquid crystal injected between a lower plate provided with pixel electrodes and an upper plate provided with color filters. The color filter includes red(R), green(G) and blue(B) unit filters on a transparent substrate, and a light-shielding layer for preventing deterioration of brightness and color purity among these unit filters. The color filter has a different configuration depending on the mode of the LCD. In the color filter used for the TN mode, a common electrode is formed on the unit filters. On the other hand, in the color filter used for the IPS mode, a protective film, instead of the common electrode, is formed on the unit filters and the light-shielding layer is made from only a resin so as to prevent an undesired affect to a horizontal electric field of the lower plate. Also, in the color filter used for the IPS mode, a transparent ground electrode for eliminating static electricity at the screen is formed at the rear surface of the transparent substrate, that is, at the surface in which the unit filters are not formed.
FIG. 1 is a sectional view showing a structural example of a conventional color filter for a TN mode LCD. Referring to FIG. 1, in the conventional color filter, a first light-shielding layer 13 formed of a metal oxide film and a second light-shielding layer 15 formed of a metal film are disposed in a lattice shape on a transparent substrate 11. The first light-shielding layer 13 may be formed of a twofold film consisting of a metal oxide film and a metal nitride film. First, second and third filters 17a, 17b and 17c for transmitting R, G and B color lights, respectively are formed at a portion in which the first and second light-shielding layers 13 and 15 on the transparent substrate 11 are not formed. The first, second and third filters 17a, 17b and 17c are made from an acrylic resin or polyimide group resin dispersed with pigments, and is separately formed on the first and second light-shielding layers 13 and 15 to prevent color mixture.
A common electrode 19 made from a transparent conductive material such as an indium tin oxide (ITO), a tin oxide (TO) or an indium zinc oxide (IZO), etc. is formed on the first to third filters 17a, 17b and 17c. The common electrode 19 allows the first to third filters 17a, 17b and 17c to not contact a liquid crystal so as to prevent its damage.
FIG. 2 is a sectional view showing a structural example of a conventional color filter for an IPS mode LCD. Referring to FIG. 2, in the conventional color filter, a light-shielding layer 23 in which a resin dispersed with an electrically insulated black pigment has a lattice shape is formed on transparent substrate 21. First, second and third filters 27a, 27b and 27c for transmitting R, G and B color lights, respectively are formed at a portion in which the light-shielding layer 23 are not formed. The first, second and third filters 27a, 27b and 27c are made from an acrylic resin or polyimide group resin dispersed with pigments, and is separately formed on the light-shielding layer 23 so as to prevent color mixture. In the case of forming the light-shielding layer 23 from a conductive material, a horizontal electric field generated from the lower plate causes drive problems due to noise generated upon drive control due to a derivative electric field generated by the conductive material.
A protective layer 25 is formed on the first to third filters 27a, 27b and 27c. The protective layer 25 plays a role isolating the first to third filters 27a, 27b and 27c from contact with a liquid crystal (to cause damage thereto), and is made from a transparent material having an insulating characteristic, such as polyimide. A ground electrode 29 is formed on the rear surface of the transparent substrate 21, that is, on the surface in which the first to third filters 27a, 27b and 27c are formed. The ground electrode 29 eliminates static electricity on a screen to prevent generation of domain stains, and is made from a transparent conductive material such as ITO, TO or IZO, etc.
However, the conventional color filter has a problem in that a step difference is generated at a portion where each of the filters overlaps by a thickness of the light-shielding layer, to cause deterioration in surface morphology. The TN mode color filter has a problem in that, when a stacked structure of a metal oxide film and a metal film is formed, pinholes are generated during the cleaning after generation of stripped particles in a continuous film formation process to thereby cause a light leakage phenomenon. The IPS mode color filter has a problem in that, since the light-shielding layer is made from only a resin and formed after formation of the ground electrode, a stain is generated due to its contact with a conveyer machine (e.g., a roller and a robot hand, etc.) upon formation of the ground electrode at the rear side of the transparent substrate, or an adhesion between the light-shielding layer and the transparent substrate is weakened to cause stain formation.
Accordingly, it is an object of the present invention to provide a color filter wherein a light-shielding layer is formed at the rear side of a transparent substrate to prevent deterioration of surface morphology.
A further object of the present invention is to provide a color filter that is capable of preventing light leakage caused by pinholes generated at a light-shielding layer.
A yet further object of the present invention is to provide a color filter that is capable of preventing stain formation caused by adhesion weakness between a light-shielding layer and a transparent substrate.
In order to achieve these and other objects of the invention, a color filter according to an embodiment of the present invention includes a light-shielding layer having a lattice shape formed from a metal material on a second surface of a transparent substrate having first and second surfaces; and first, second and third filters, being formed at a portion which does not correspond to the light-shielding layer on the first surface of the transparent substrate in such a manner so as to have a desired portion overlapped with the light-shielding layer, to transmit red, green and blue color lights, respectively.